1. Field of the Invention
The invention relates to a threaded pipe connector.
2. Description of the Related Art
A typical threaded pipe connector used in petroleum and natural gas industry generally includes thread, seal, and torque shoulder, which are modified constantly over years to meet design requirements for strength and airtight.
For designing threaded sleeves with big caliber, thick-wall, and high grade steel, using only API buttress thread may lead to pull-out failure, so it's extremely important to choose optimal ratio of thread flank angle and thread height to pitch.
Coupling threads fall into two categories: single stage seal and multistage seal in term of sealing design. Sealing interference, sealing length or both shall be increased to ensure high performance sealing, which requires high processing precision and has tendency to galling. Multistage sealing can reduce drawbacks of single stage sealing, but two sealing faces are not separated in conventional multistage thread configuration, it makes no difference with single stage seal in performance, and sacrifices reliability. Sealing surfaces are separated in the multistage shoulder with double torque shoulder, but processing is very difficult and yield is pretty low.